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Kōaro

A remarkable native freshwater fish of Aotearoa New Zealand

Physical Characteristics

Kōaro (Galaxias brevipinnis) are a native freshwater fish found throughout Aotearoa New Zealand. They typically grow between 150 and 250 millimetres in length, with some individuals reaching up to 300 millimetres.

Kōaro have long, slender bodies with a mottled brown, olive, or golden colouration that provides excellent camouflage against rocky streambeds and leaf litter. Their streamlined shape and strong fins make them powerful swimmers in fast-flowing water.

Habitat and Distribution

Kōaro are found in a wide range of freshwater habitats, including streams, rivers, lakes, and wetlands, from lowland catchments to steep upland forest streams. They are especially common in cool, clear, fast-flowing waterways with rocky substrates and good riparian cover.

Unlike many other galaxiids, kōaro are often found high in catchments and above waterfalls, thanks to their exceptional climbing ability as juveniles.

Life Cycle

The life cycle of Galaxias brevipinnis is typically diadromous, meaning kōaro migrate between freshwater and the sea. Adults live in freshwater but migrate downstream to spawn in rivers and estuaries, usually during autumn and winter floods.

The eggs hatch into larvae that are swept out to sea, where they spend several months feeding as part of the plankton. In spring, the juveniles return to freshwater as part of the whitebait run.

These juvenile kōaro are strong climbers and can scale waterfalls and steep rock faces, allowing them to reach headwater streams that are inaccessible to most other fish.

Diet and Feeding Behaviour
Aquatic Insects

Insect larvae and adult aquatic insects form a major part of their diet

Invertebrates

Worms, small crustaceans, and terrestrial invertebrates that fall into the water

Night Hunters

Active predators that feed mainly at night

Their large mouths and sharp teeth make them efficient hunters in fast-flowing, rocky streams.

Ecological Importance
Role in Food Webs

Ecologically, kōaro play an important role in freshwater food webs as both predators and prey. They help regulate invertebrate populations and provide food for larger fish, eels, birds, and trout.

Ecosystem Indicators

Because they depend on clean water, intact riparian vegetation, and unimpeded migration routes, kōaro are strong indicators of healthy freshwater ecosystems.

Environmental Pressures

Despite their wide distribution, kōaro face several environmental pressures.

Habitat Degradation

Habitat degradation from deforestation, farming, urban development, and sedimentation reduces water quality and stream stability.

Migration Barriers

Barriers such as dams, culverts, and weirs block migration routes and prevent juveniles from reaching upper catchments.

Introduced Species

Introduced species, especially trout, compete with and prey on kōaro in many waterways.

Conclusion

In conclusion, kōaro (Galaxias brevipinnis) are a highly adaptable and ecologically important native fish in New Zealand's freshwater ecosystems.

Their remarkable climbing ability, complex life cycle, and reliance on healthy rivers highlight the importance of protecting catchments, restoring fish passage, and maintaining clean water to ensure the long-term survival of kōaro across Aotearoa.